1. Field of the Invention
The present invention relates to a novel silver halide color light-sensitive material, in particular, a novel light-sensitive material adapted to a heat development process (hereinafter may be referred to merely as a light-sensitive material) and a method of forming color images utilizing said light-sensitive material.
2. Description of the Related Art
Owing to remarkable development of light-sensitive materials utilizing silver halides, high-quality color images are now easily obtainable. For example, according to ordinary color photography, a color print is obtained by the process comprising taking a photograph utilizing a color negative film, developing the film, and printing the image information, which is recorded in the color negative film, on color photographic paper in an optical way. Recently, this process has made remarkable progress, and large-scale, color development laboratories, in which a large quantity of color prints are produced in a very efficient way, have spread along with the so-called mini-laboratories which are now in shops and are designed to provide small-scale, handy printer processing. Therefore, anybody can enjoy color photography easily.
The color photography, now in common use, reproduces color by the subtractive color process. Generally, a color negative film comprises a transmittable substrate and light-sensitive layers thereon utilizing a silver halide emulsion as a light-sensitive component having a sensitivity to the blue, green or red wavelength region of light, and a so-called color coupler capable of producing a yellow, magenta or cyan dye as a complementary hue of the sensitive wavelength region of the layer. A color negative film, which has been exposed while taking a photograph, is developed in a color developer containing an aromatic primary amine developing agent. In this process, the developing agent develops, i.e., reduces the exposed silver halide grains, and the oxidation product of the developing agent, which are formed concurrently with the forgoing reduction, undergoes the coupling-reaction with the color coupler to form a dye. The silver (developed silver) generated by the development and the unreacted (unexposed) silver halide are removed by means of a bleaching process and fixing rocess. This creates a color image on the color negative film. Consequently, a color photographic paper which comprises a reflective substrate and light-sensitive layers formed thereon having the same combinations of light-sensitive wave length region and hue to be produced as in the color negative film, through the developed negative film, and color-developing, bleaching and fixing the color photographic paper in the same manner as in the case of the negative film to obtain a color print having a color image as a reproduction of an original image thereon.
Although these systems are widely adopted at the present time, there is a growing demand for a simpler system. First reason for this is that expertise and skilled operation are necessary, due to the requirement of strict control of the composition and the temperature of the processing solution in a processing bath for the above-mentioned procedure consisting of color development, bleaching and fixation. Second reason for this is that closed equipment exclusively for the use in the developing process is often required, due to substances, such as a developing agent and an iron chelate compound, the discharge of which is regulated from the standpoint of environmental protection, contained as a bleaching agent in the processing solution. Third reason for this is that the currently available system does not perfectly fulfill the requirement for a rapid reproduction of image, as the above-mentioned developing process still requires a long time, although the time is shorted by the recent advance in technology. Based on this background, there has been a strong demand for a simpler system which does not utilize the developing agent and bleaching agent now in use for a conventional color image forming system and which accordingly minimizes the adverse effect on the environment.
In light of the aforementioned problems, various improved techniques have been proposed. Particularly, diverse techniques which utilize heat development have been proposed in order to achieve simple and rapid developing step.
Heat-developable light-sensitive materials and a process for their development are described in, for example, published by Shashin Kogaku no Kiso--Higin'en Shashin ("Fundamentals of Photographic Engineering--Non-silver Salt Photography"), Corona Publishing Co., Ltd. (1982), pp. 242-255.
Also, many methods of obtaining color images through heat development have been proposed. For example, a method of forming color images through the coupling of an oxidized product of a developing agent with a coupler is proposed in U.S. Pat. Nos. 3,531,286, 3,761,270, and 4,021,240, Belgium Patent No. 802,519, and Research Disclosure (hereinafter abbreviated as RD), pp. 31-32 (Sep. 1975).
However, the aforementioned methods require a relatively long time for development, and images obtained thereby are highly fogged and low in image density.
Also, IS & T's 48th Annual Conference Proceedings, pp. 180, discloses a system in which the dye formed in the developing reaction is transferred to a mordant layer and thereafter stripping a light-sensitive material from an image receiving material bearing the mordant layer to separate the developed silver and unreacted silver halide from an image formed by the dye without the use of a bleaching-fixing bath which has been indispensable to a conventional photographic process. However, this technique cannot perfectly solve the environmental problems, because it still needs a developing process by use of a processing bath containing a developing agent.
Fuji Photo Film Co., Ltd. has proposed a Pictrography System and the Pictrostat System which dispenses with a processing solution containing a developing agent. In this system, a small amount of water is supplied to a light-sensitive material containing a base precursor which reacts with water to generate a base. The light-sensitive material and an image receiving material are placed face to face and heated to promote the developing reaction. This system does not use the aforementioned processing bath and, in this regard, is advantageous with respect to environmental protection. However, in these systems, the thus-formed dyes are fixed in a dye-fixing layer to thereby form dye images to be viewed. Therefore, it has been desired to develop a system capable of applying this technique to recording materials for photographing use.
Since silver halide light-sensitive materials for photographing use must have high sensitivity, improving the sensitivity of silver halide grains is essential. To attain this end, preferably tabular silver halide grains have been used.
There have been proposed various kinds of silver halide grains suited for a heat development system wherein development is performed at high temperature. For example, Japanese Patent Application Publication (JP-B) No. 2-48101 discloses a technique for improving the progress in heat development step through the use of a heat-developable light-sensitive material containing tabular silver halide grains whose diameter is at least 5 times the thickness thereof. Also, Japanese Patent Application Laid Open (JP-A) No. 62-78555 discloses a technique for improving long-term storage stability of a heat-developable light-sensitive material through providing therein tabular light-sensitive silver halide grains whose silver iodide content is 4-40 mol % and which have a diameter-to-thickness ratio of 5 or greater in an amount of 0.05-1 mol with respect to 1 mol of organic silver salts. Further, JP-A No. 62-79447 discloses a technique for improving sensitivity and maximum density at the time of heat development through combined use of tabular light-sensitive silver halide grains having a diameter-to-thickness ratio of 5 or greater and light-sensitive silver halide grains having a silver iodide content of 4-40 mol % and a mean diameter of 0.4 .mu.m or less.
However, these techniques are intended for use in light-sensitive materials for printing use. Therefore, it has been desired to develop a system capable of applying these techniques to recording materials having sufficient sensitivity for photographing use. Also, these emulsions have been experimentally applied to the aforementioned heat development system in an attempt to obtain a light-sensitive material for photographing use which can be processed in a simple, quick manner. However, the experiments revealed that the use of tabular grains tended to impair mar resistance, indicating a potential problem in practical use.
In order to prepare a light-sensitive material for photographing use through the use of the above-mentioned system, a silver halide emulsion to be used must have higher sensitivity.
One technique for improving sensitivity of a sliver halide emulsion is to use tabular sliver halide grains.
With regard to tabular grains used in ordinary solution development type photographic systems, methods for their preparation and techniques for their use are disclosed in, for example, U.S. Pat. Nos. 4,434,226, 4,439,520,4, 414,310, 4,433,048, 4,414,306, and4,459,353, JP-A Nos. 59-99433 and 62-209445.
Studies have been conducted on the use of the tabular grains disclosed in the above publications in order to obtain a color light-sensitive material which contains a color developing agent and which enables simple image recording, and these studies have revealed that granularity of the attempted system is poorer than that of a conventional color negative development system. Also, an attempt to meet the demand that color light-sensitive materials have high sensitivity resulted in fog formation, poor picture quality, and a tendency toward an increase in fog formation in light -sensitive materials during their storage.